Hey there!!
You click on the image and got up to the top of the screen and click on "object - arrange - send to back" NOT "SEND BACKWARD".
Hope this helps. c:
Answer:
Glass is the most common material used to construct lens elements, due to its good optical properties and resistance to scratching. Other materials are also used, such as quartz glass, fluorite, plastics like acrylic (Plexiglass), and even germanium and meteoritic glass.
uhm.......ok then..............
